In recent years, light-emitting devices configured to employ solid light-emitting elements such as light emitting diodes (LED) or semiconductor lasers (LD; Laser Diodes) as excitation light sources and use, as illumination light, fluorescent light generated by irradiating a light-emitting section, which includes a phosphor, with excitation light generated from such excitation light sources have been more intensively studied.
It is necessary that such light sources which excite the phosphor by using solid light-emitting elements meet eye safety requirements provided in International Safety Standards IEC60825-1 and JIS C6802 and the like in Japan. It is desired to obtain a Class1 level of eye safety, in which there is no concern of loss of sight even if illumination light emitted from the light sources is directly incident on eyes via certain optical systems, mainly for applications of consumer equipment such as an illumination device.
Particularly, it is necessary to increase an apparent light source size (light-emission spot size) of laser light emitted to the outside of an illumination device in order to enhance eye safety. In addition, it is also necessary to reduce coherence of laser light.
PTL 1 discloses a light source device, in which a phosphor layer receiving excitation light and emitting fluorescent light is attached by minute concavity and convexity. More specifically, a light-emitting wheel, in which a thin diffusion layer is formed on a laser light irradiation side of a circular substrate and a phosphor is bonded to a side opposite to the laser light irradiation side is disclosed.
Next, PTL 2 discloses a light source device, in which laser light from a semiconductor laser element is diffused by a diffusing lens and then a phosphor converts the diffused light into visible light. More specifically, a technique of diffusing laser light by a diffusing lens and irradiating a phosphor with the diffused laser light is disclosed.
Next, PTL 3 discloses a flash device with a reflective plate which is composed of a laser light scattering member for uniformly scattering laser light from a semiconductor laser and coated with a plurality of types of phosphors emitting red, green, and blue fluorescent light. More specifically, a technique of scattering a laser light flux emitted from a semiconductor laser by a reflective plate is disclosed.
Next, PTL 4 discloses a light-emitting device, in which an opening capable of outputting light from a semiconductor laser element is disposed in a region different from a center axis of a light guiding member optically coupled to the semiconductor laser element and a wavelength conversion member absorbing at least part of the light from the semiconductor laser element and generating light with different wavelengths is provided between an end of the light guiding member and the opening. More specifically, according to the technique disclosed in the patent literature, an opening of a cap for protecting a light guiding member is provided in a region other than a region which coincides with a center axis of the light guiding member for guiding laser light, the laser light is diffused by an inner wall of the cap in the region which coincides with the center axis, and the laser light is changed to random light with a low coherence property.